This invention relates to improved tape guidance in a magnetic tape data cartridge.
Magnetic tape cartridges for tape carrying digital data on a number of tracks across the tape are well known. Tape cartridges include a cartridge shell that defines an enclosure, and a pair of tape reels supported within the enclosure. A length of magnetic tape extends along a tape path within the enclosure. Each end of the tape is wound onto one of the reels. The tape moves past suitable guides and across an opening in an edge of the cartridge into which a read/write head or transducer protrudes to tension the tape and write or read data when the cartridge is inserted into a recording/reproducing machine. The tape is driven by a belt so that the linear tape speed is controlled precisely.
In order to maintain the tape properly positioned so that each of the very narrow individual tracks of data is appropriately positioned as it crosses the read/write head, it is important that the tape be guided precisely along its path of travel. The clearance required between conventional guide flanges for accommodating the maximum allowable tape width within manufacturing tolerance is great enough so when the tape width varies to its minimum allowable tolerance tape width, the tape will be permitted to wander in direction laterally of the tape sufficiently to cause read/write problems when the data tracks are increased significantly in density using existing guides provided in magnetic tape cartridges.
A tape that is one-quarter inch wide (6.35 mm), using present guides, may have up to 32 tracks across the width of the tape. It is desirable to increase the density up to the range of 50 to 60 tracks on a one-quarter inch tape, utilizing a standard data cartridge. Tape speeds are now in the range of 0.5 meters per second to 3 meters per second.
Servo-drives are also used for positioning a tape under positive control, but such drives are expensive. The present invention aids in reducing the band width of tape control in servo-drives as well as reducing the complexity, and thus cost, of such drives.
Thus, the ongoing need to store increased quantities of data on a given quantity of magnetic tape, along with the development of recording heads which are capable of recording narrower tracks at ever smaller spacings has led to the need for more precise positioning of magnetic recording tape relative to the heads during recording and playback.
Magnetic tape cartridges of the type disclosed in for example, U.S. Pat. No. 5,104,058, provide precisely located reference surfaces in the form of flanged guide pins for positioning an edge of the tape relative to the head, at selected points along its path, and means for urging the tape into engagement with the flanges so as to position the tape, and hence the tracks of recorded data relative to the head. The function of urging the tape into engagement with the guide pin flanges results from the angle at which the flanged guide pins are inserted into the baseplate. By inserting at least one of the guide pins into the baseplate with a slight deviation from perpendicularity with the baseplate, a steering effect which urged the tape into engagement with particular flanges of the guide pins is provided to the data tracks relative to the head.
Flanged cylindrical tape guides have the additional advantage being able to be manufactured to a high degree of precision, since they can be produced on an automatic lathe, or screw machine.
Other tape guides for positioning the tape as it passes a magnetic head are also known. U.S. Pat. No. 5,251,844 discloses a compliant tape guide which provides a reference surface contacting one edge of a magnetic recording tape, and a moveable, or compliant member contacting the opposite edge of the tape, thereby urging the tape against the reference surface. Other complaint guides are disclosed in, for example, the following IBM Technical Disclosure Bulletins:
Vol. 14, No. 2, July, 1971, p. 399 PA1 Vol. 15, No. 8, January, 1973, p. 2502 PA1 Vol. 25, No. 1, June, 1982, pp. 444-446 PA1 Vol. 25, No. 1, June, 1982, pp. 447-448 PA1 Vol. 25, No. 2, July, 1982, pp. 809-810 PA1 Vol. 25, No. 4, September, 1982, p. 2069 PA1 Vol. 26, No. 7A, December, 1983, p. 3398 PA1 Vol. 27, No. 7B, December, 1984, pp. 4360-4361 PA1 Vol. 29, No. 5, October, 1986, pp. 2126-2127 PA1 Vol. 31, No. 3, August, 1988, pp. 232-233 PA1 Vol. 32, No. 3B, August, 1989, pp. 175-176 PA1 Seitzinger, R. C., "Coatings that Cut Friction," MACHINE DESIGN, Oct. 21, 1976, pp. 114-119. PA1 Covino, C. P., "Hard Coat Plus Solid Lube Fights Wear Problems," METAL PROGRESS, June, 1975, pp. 69-70.
While the compliant guides disclosed in these references represent a variety of configurations for urging one edge of a travelling magnetic tape against a reference surface by applying force, through a compliant guide, against the opposite edge, they share a common feature, in that in all cases, the tape travels in an arcuate path around the guide while the guiding force is being applied.
The need to provide an arcuate path is further cited in U.S. Pat. No. 5,173,828, at column 4, lines 10-26, wherein it is explained that even though the tape is very thin, and hence not stiff in the transverse direction, it becomes relatively rigid when formed into a longitudinal arc, thus enabling the force of the compliant guide to press against the edge of the tape without buckling the tape.
A tape guide which engages the edges of the tape over a longer distance, thereby enabling a lubricating air film to form, so as to reduce frictional drag on the tape, is disclosed in EP 536 912, assigned to Minnesota Mining and Manufacturing Co. In addition, the longer engagement length serves to damp out vibrations and other transport deviations which might otherwise result from conditions upstream from the guide, such as tape reel eccentricity.
The tape guide also must be highly abrasion resistant, since magnetic recording tape is inherently abrasive. In IBM Technical Disclosure Bulletin Vol. 29, No. 5, October, 1986, wear resistant pads are used to contact the edge of the tape in a compliant guide system, thereby enabling the material for the spring portion of the compliant guide to be chosen without trading off spring properties for wear properties.
Surface coatings for imparting wear resistance to surfaces which might not otherwise resist wear are known. U.S. Pat. No. 4,594,772, for example, discloses a hard anodize coating which is resistant to wear caused by transport of magnetic tape.
In addition, dry lubricants can be incorporated into wear resistant anodized coatings for the purpose of reducing friction. Such coatings are described in the following references:
The present invention provides advantages of a compliant guide for one edge of a tape in a magnetic tape cartridge that is usable with existing recording/reproducing machines.
None of these references have a compliant guide used in the existing, standard belt driven tape cartridges. The addition of a compliant guide to the standard belt driven magnetic tape cartridge provides better tracking of the tape. The compliant guide applies a controlled amount of load on the tape edge without adversely disturbing the tape tension or tape slope. The tape is permitted to ride against a reference guide surface in the region where the tape is formed into a longitudinal curve.